In the usual PCM (pulse-code-modulation) telephone or other telecommunication system, such a frame period may be divided into 32 time slots assigned to respective signal channels including, say, 30 voice channels and two service channels; thus, a group of 32 channels is allotted to each signal path. Each time slot generally has a duration of approximately 4 .mu.s equaling--with 8-bit coding of digitized voice samples--eight bit intervals of 500 ns duration. The temporal ad/or spatial transposition enables the transfer of voice samples or supervisory signals from any incoming channel to any outgoing channel, on the same or a different signal path, communicating therewith.
A switching unit or symmetrical time-division matrix (STM) of this type has been disclosed, for example, in U.S. Pat. Nos. 4,093,827 and 4,154,982. As particularly described in the first one of these patents, a series/parallel converter concurrently receives during each time slot the serially arriving bits of respective bytes from eight incoming signal paths or junctions which are then transmitted in parallel, one byte at a time, to a speech memory for temporary storage in respective cells thereof. The readout from the memory, under the control of address instructions from an external source acting as a telephone marker, occurs by way of a serializer receiving the bits of each byte in parallel from the memory and delivering them sequentially, during a designated time slot, to the outgoing signal path or junction for which they are intended.